Here is a tutorial on how to submit to publications that you are already added as a writer on: https://medium.com/new-writers-welcome/how-to-publish-to-a-publication-4b2725f66941

This is useful: https://medium.com/new-writers-welcome/dear-writers-of-new-writers-welcome-8cfec62dcc9e

And there's a whole help section in New Writers Welcome. Select it from the menu on the home page.

I can also compile a list of publications that are accepting new writers and share it in New Writers Welcome.